Coordination entities of a Pyrene-based Iminopyridine ligand: Structural and photophysical properties

Abstract : A pyrene-based iminopyridine ligand L has been prepared and displays the absorption and emission properties expected for pyrene-based derivatives in solution. Ligand L, as well as two neutral and one monocationic coordination entities, respectively formulated as [ZnLCl2] 1, [ReLCl(CO)3] 3 and [CuL2](BF4) 2, have been crystallized and analyzed by single crystal X-ray diffraction analysis. The corresponding crystal structures indicate the formation of supramolecular architectures generated by offset π···π stacking between pyrene fragments and strong C-H···π interactions in coordination entity 1. For the cationic coordination entity 2, the crystal packing reveals the presence of C-H···F and C-H···π interactions and numerous C-H···π contacts interconnecting the molecules into a 3D network. As for coordination entity 3, hydrogen bonding and π···π stacking link the molecules in a three dimensional manner. Zinc (II) and copper (I) coordination entities have also been studied through isothermal titration calorimetry, which indicate a strong binding and a different stoichiometry for both coordination entities. Photophysical studies of the ligand and corresponding coordination entities show a monomer type pyrene emission and a higher fluorescence quantum yield for the zinc coordination entity 1 as compared with copper 2 and rhenium 3 coordination entities.